1. Field of the Invention
2. General Background and State of the Art
This invention relates to the treatment of body lumens and, more particularly, to the endovascular placement of medical devices within vasculature for the purpose of repairing the same.
Ruptured abdominal aortic aneurysms (AAA) are a leading cause of death in the United States. Treatment options to repair AAA include conventional open surgery and implantation of an endovascular graft. Conventional open surgical repair of AAA involves major abdominal surgery with associated high rates of morbidity. Endovascular grafts have been developed to endoluminally bypass abdominal aortic aneurysms through minimally invasive surgery. Many patients that are unacceptable surgical risks for open repairs are eligible for endovascular graft implantation. Deployment of transfemoral, endovascular grafts to treat AAA is appealing for many reasons: avoidance of an abdominal incision, lack of aortic cross clamping, the potential for regional anesthesia, and a shortened hospital stay.
Untreated AAA have been shown to continue to expand until rupture, with an associated high mortality rate. Implantation of endovascular grafts have also been associated with high complication rates, including perioperative death, conversion to open repair, the need for further intervention, the need for hemodialysis, a failure to cure the AAA, and wound complications.
The inability to obtain or maintain a secure seal between the vessel wall and the endovascular graft is a complication unique to endovascular aneurysm exclusion. Because the term “leak” has been associated with aneurysm rupture following conventional surgery, the term “endoleak” has been proposed as a more definitive description of this complication. It is believed that persistent endoleaks result in continued aneurysm expansion, which may eventually lead to aneurysm rupture. Aneurysms that have been successfully excluded have shown a tendency towards a reduction in aneurysm diameter. Failure to properly exclude the aneurysm from systemic arterial blood pressure keeps the patient at risk of impending rupture. Endoleaks have been classified according to the source of the leaks. Current classifications of endoleaks include four categories. Type I endoleaks are “perigraft” or “graft-related” leaks that involve a persistent channel of blood flow due to inadequate or ineffective sealing at the ends of the endovascular graft, or between overlapping components of a modular system. Type II endoleaks are retrograde flow into the aneurysm sac from patent lumbar arteries, the inferior mesenteric artery, or other collateral vessels. Type III endoleaks result from fabric tears, graft disconnection, or graft disintegration. Finally, Type IV endoleaks are flow through the graft fabric associated with graft wall porosity or permeability. It has been recognized that preoperative patent side branches are not a good predictor of postoperative endoleaks.
There have been a number of reported cases of aneurysm rupture following implantation of an endovascular graft. Some of the ruptures occurred in patients without a documented endoleak.
A number of studies have focused on measurement of pressure within the aneurysm sac following implantation of an endovascular graft, both in the human patient, an animal model, or an in vitro model. Properly implanted endovascular grafts have been shown to reduce the pressure within the aneurysm sac while an endoleak, with or without detectable blood flow, continues to pressurize the sac at pressures equivalent to the systemic arterial pressure. Animal studies utilizing a predictable rupturing aneurysm model have shown that non-excluded aneurysms will rupture. Thrombosed aneurysm sacs may still receive pressurization from a sealed endoleak and this continued pressurization keeps the aneurysm at risk for rupture.
Current methods of patient follow-up include arteriography, contrast-enhanced spiral computed tomography (CT), duplex ultrasonography, abdominal X-ray, and intravascular ultrasound. All of these methods are costly and involve invasive procedures with associated morbidity that may need to be performed in a hospital. None of the imaging methods are completely successful in detecting endoleaks. Therefore, the potential exists for an endoleak to go undetected until eventual rupture. An increase in aneurysm diameter is detectable, and should be considered an indication of endoleak. To avoid aneurysm rupture an increase in aneurysm diameter must be detected in a timely fashion to identify patients in need of corrective endovascular procedures.
An endovascular graft with the ability to measure pressure within the aneurysm sac and provide feedback to the physician could provide acute confirmation of a procedure and identify those patients with persistent pressurization of their aneurysm, and subsequent risk of rupture. Some physicians are advocating that the follow-up examinations of AAA patients focus on pressure measurements, but that this is not currently clinically feasible. Furthermore, follow-up examinations may be performed in the physician's office as opposed to a hospital. Moreover, clinicians will require method to study the pathology of post-endovascularly treated AAA disease.
Accordingly, there exists a need for a non-invasive measurement of pressure, as well as other pertinent parameters, within the aneurysm sac as a means for confirming the success of a procedure as well as identifying patients at risk for aneurysm rupture after the endovascular graft is implanted.
However, providing devices on an endovascular graft to facilitate the measurement of pertinent parameters poses problems. The measurement device increases bulk, which can significantly affect the delivery profile of the endovascular graft and increase the force necessary to deploy the device, such as jacket or release wire retraction forces. Thus, increased bulk is a significant issue for an endovascular graft. Furthermore, attachment of measurement devices to an endovascular graft may require sutures and the suture knots not only provide increased bulk, but are also potential graft wear points. Additionally, tissue growth around a measuring device attached to an implanted endovascular graft may interfere with its function and inaccurate data may result.
Therefore, what is need are alternative approaches to obtaining information regarding the success of an aneurysm repair procedure such as alternative approaches to gaining access to delivering and implanting sensing devices to the repair site. The present invention addresses these problems and other needs.